UNIVERSITY OF SOUTH AUSTRALIA School of Engineering

EEET 1026 

Introduction to Computer Systems  

Practical 1 

   OCCUPATIONAL HEALTH &  SAFETY WORKSHOP 

Reference Materials 

This manual represents modified exerts from the book Occupational Health and Safety in the Laboratory, Fullick, Krajniak & Barker, Harcourt Brace,1996 ISBN 0 7295 3288 7 Occupational Health & Safety Workshop – 1st Year Students

1  

1 HAZARD IDENTIFICATION AND RISK ASSESSMENT

PURPOSE

To enable the learner to correctly identify laboratory hazards, to find information relating to them, and to assess the risk posed by particular hazards in the workplace. This chapter addresses the following learning outcomes

ascertain the hazards associated with specific materials, equipment and procedures involved in laboratory operations recognise laboratory hazards and perform appropriate risk assessment procedures identify workplace hazards and estimate their level of risk.

1.1 INTRODUCTION

Hazard refers to the potential of something to cause harm.

It may be associated with the use of a substance which is inherently hazardous, or it may be caused by workplace organisation, or even a poorly designed component or procedure. If you use the term to describe something then you must also qualify the degree of hazard. For example a chemical substance may cause a skin rash (not very hazardous) or it may kill almost instantly (extremely hazardous). However, very hazardous substances may pose little risk to a person's health, if they are used in a safe manner.

Risk refers to the likelihood of a person being injured in a given situation.

The risk associated with the use of a substance or procedure depends on a number of factors. For example, in the case of a hazardous substance it will depend on:

what the substance is made of how much is being used what it is being used for in the workplace.

The risk associated with the use of a small portable gas cigarette lighter used by a non- smoker to light camp fires would be classified as very low even though it contains a highly flammable substance. This is because it is infrequently used and contains a small volume of the substance. By contrast, the risk associated with the transfer of bulk liquid petroleum gas from a large storage tank to a road transport tanker at a supply terminal would be very high as large amounts of (the same) flammable substance. are involved and the procedure would occur frequently. Hence the chances of something going wrong increase greatly. If the degree of hazard associated with a given procedure or substance is well known, then measures can be taken to minimise the risk associated with the hazard. If you are aware of the hazards, you can minimise your chances of being injured. Two terms which you are likely to encounter in any risk assessment work are epidemiology and occupational hygiene. Epidemiology refers to the use of statistics to link occupational sickness or accidents to workplace procedures to try to identify high risk areas. Persons who undertake these studies are referred to as epidemiologists. They normally act on larger samples of the workforce or population in order to identify problem areas for occupational health authorities to target for education campaigns, or workplace studies to improve procedures. Occupational hygiene refers to the evaluation of hazards with the goal of controlling them through procedures such as personal protective equipment, engineering controls, education and monitoring of the environment. Occupational hygiene issues will be dealt with in this chapter and the following one.

1.2 RECOGNITION OF HAZARDS

There are many different types of hazards encountered in the workplace. For the purposes of

2  

simplicity, these may be categorised into groups associated with particular areas or workplaces. 1.2.1 Chemical Hazards Chemicals are an important part of every aspect of our daily lives. It is impossible to prevent some exposure to chemical substances in our society, so they pose probably the greatest risk to occupational health. There are over 100 000 commonly available chemical substances used in this country, with the number likely to increase in the future. Those in highly volatile forms such as gases, vapours and dusts generally pose the greatest risk, but solid or liquid materials may be highly flammable, corrosive or even explosive and should be used with care.

1.2.2 Biological Hazards This category refers to infectious materials such as viruses, bacteria and fungi. Biological materials can be extremely hazardous as they are capable of reproduction and transmission. This means that a person may be infected by only a small amount of hazardous material, and transfer it to many others - even those outside the workplace.

1.2.3 Physical Hazards These include aspects of the environment such as noise, lighting levels and temperature. They greatly affect worker performance through influencing the comfort level of the workplace. A better physical environment will, in general, increase productivity and decrease problems such as eyestrain and hearing loss.

1.2.4 Ionising and Non-lonising Radiation Hazards This category includes all forms of radiation such as ultraviolet, infra-red, microwave, X-ray, radioactive isotopes, etc. The former three are called non-ionising radiation as they do not cause direct chemical changes in the body cells of people who are exposed to them; while X-rays, and radiation from radioactive substances (and in some circumstances strong ultraviolet) are known as ionising as they affect chemicals in cell tissue, changing them into more highly reactive chemicals. This means they can be destructive to human tissue. 1.2.5 Psychosocial stresses This refers to shift work, personal stress and other social stresses which affect both a worker's psychological wellbeing and health in general. Stress is the plague of the modern workplace. It is caused by our rapid leap from the primitive lifestyles of our ancestors to modern high-paced social structures without the necessary evolutionary change.

1.2.6 Ergonomics and Manual Handling Ergonomics involves the fitting of tools and procedures in the workplace to the worker. Many pieces of equipment in the workplace are designed to be process friendly. This often means that they were not designed to fit the worker, but instead based on cheapest cost or easiest-to-repair principles. The result is equipment that is hazardous to the worker, such as older types of computer desks which led to many cases of repetitive strain injuries (RSI - now referred to as occupational overuse syndrome, or OOS).

Manual handling of items in the workplace is at present an unavoidable aspect of work. Some items are heavy or difficult to lift however, and should be moved using special procedures. Often these procedures are overlooked or viewed as `not macho', and as a result many people suffer injury (especially of the back).

3  

1.3 SOURCES OF OCCUPATIONAL HEALTH AND SAFETY INFORMATION

There are now many reliable and freely available sources of occupational health and safety information. If you know little about occupational health and safety, then this section will highlight some of the more important sources, particularly with respect to hazardous substances. For greater detail, you should consult the recommended reading, or contact your local occupational health and safety authority.

The University Libraries hold copies of the OCCUPATIONAL HEALTH, SAFETY AND WELFARE ACT 1986 and OHS&W REGULATIONS 1995. The Act and Regulations are also available on the University’s OHSW Web page at http://w3.unisa.edu.au/safetyandwellbeing/legislation/default.asp. The library also holds copies of Australian Standards.

1.3.1 Material Safety Data Sheets (MSDS’s) These are fact sheets which provide the information required to allow the safe handling of materials in the workplace (or any other location). They provide information such as: the identity of the substance its physical and chemical characteristics any potential health risks associated with its use correct instructions on how to use and dispose of the substance storage information any special codes for emergency services in case of a mishap when using the

substance. There are currently no recommended requirements for the format or supply of MSDS’s for non-hazardous substances, but most responsible suppliers will provide these upon request.

MSDS’s are available in the School of Engineering for all materials used in the laboratories. The technical staff responsible for individual areas keep copies of MSDS’s that are available to all staff or students working in that area. In some cases MSDS’s are posted near materials that are used in Practical exercises, or extracts are printed in Practical notes distributed to students.

1.4 ERGONOMICS AND MANUAL HANDLING

1.4.1 Ergonomics Ergonomics is the study of the physical relationship between people and the equipment they use in the workplace.

The aim of any ergonomic study is to design a workplace that fits the worker; this is the reverse of what has occurred in the past where the flow of materials was the principal concern. The impetus for ergonomic studies has been the huge upsurge in repetitive strain and back injuries in the workplace in recent years. Studies have found that redesigning tools, equipment and work practices so that they are more suited to the anatomy of the average person, not only decreases occupational injury, but increases productivity as well. This is because ergonomically designed systems are often more efficient as well as making the worker more comfortable and less prone to injury. A good example of this is the ergonomic workstation designed for those who work on computers.

Ergonomic studies have also been used to improve the fit and comfort of clothing and personal protective equipment worn in the workplace. This has had very positive effects as protective clothing and equipment that is comfortable is much more likely to be worn by the worker, or where this equipment is compulsory, causes less stress to the wearer. When assessing a workplace for hazards it is important to remember that poor ergonomic practices probably cause more occupational illness and injury than hazardous chemicals, so careful examination of workplace procedures should be part of any safety inspection.

4  

1.4.2 Manual Handling Regulations Manual handling refers to any activity where force is used to move, hold, restrain, push, pull, lift, lower or carry an object, person or animal. Inadequate or incorrect methods for manual handling are a major source of workplace injury and illness. Because of this, Worksafe Australia has published a national standard 17 and code of practice for manual handling, 18. These have been incorporated into state occupational health and safety acts as regulations and therefore operate as law in the states (for example in SA see OCCUPATIONAL HEALTH, SAFETY and WELFARE REGULATIONS 1995, Div 2.9 Manual Handling).

The national standard for manual handling requires that employers must: • ensure that all workplace procedures, equipment, containers and plant are optimised to prevent

manual handling injuries • provide training as required to prevent workplace manual handling injuries.

Employees must:

use team lifting procedures, mechanical lifting aids, protective equipment and procedures devised in training whenever it is appropriate.

One of the key factors with the manual handling regulation is that a consultative approach is required. The aim of this is to ensure management has first-hand knowledge of workplace procedures and the manual handling risks associated with them, and to be able to involve the employees in devising strategies to overcome them. The code of practice lists the following three stages as methodology for reduction of manual handling injuries.

1. Risk identification through:

• consultation with employees • analysis of injury records • observation.

2. Risk assessment by examining: • the work environment • workers' actions and movements • worker skills and experience • clothing worn in the workplace • the age and physical condition of the worker • working posture and position of the worker • locations of equipment, and loads, and distances moved by loads • duration and frequency of manual handling • any special workplace needs or other relevant factors.

3. Risk control is undertaken by: • job redesign (such as task modification, team lifting, changing workplace layout, or

changing the shape or orientation of workplace materials, objects or equipment) • training (in correct manual handling techniques) • provision of mechanical handling aids • providing any special administrative controls

1.5 SAFETY AUDITS AND CHECKLISTS

One of the tasks of members of occupational health and safety committees is to carry out workplace inspections. These so-called safety audits are carried out in order to: • spot hazardous procedures or situations in the workplace • assess the risk they pose to worker health, and rank them in a priority

order of seriousness so that resources can be directed to the most serious problems first

• recommend changes which will lower or remove the risk.

5  

This can be a daunting task, particularly in a large workplace. You can help your safety

committee by carrying out safety audits in your own work area. A careful inspection using a standard safety checklist will help by ensuring that all potential hazards are identified as quickly as possible and the risk they pose is assessed. Many of the hazards which you find after going through a safety audit may be fixed by simple procedural changes, but others may require financial input (which requires management involvement). or technical advice. Members of your safety committee or your safety Occupational Health and Safety in the Laboratory representative should be able to direct you to the correct source of any technical advice required. If not, consult your local occupational health and safety authority.

1.5.1 How do I Recognise a Safety Hazard? In many cases this is easy. Look for: • untidy work areas • the use of damaged or inappropriate tools • poor lifting or manual handling techniques • failure to follow established safe

procedures • incorrect use of, or failure to use

protective equipment.

Look for the signs!

The identification of hazardous substances in the workplace is often a more difficult task, requiring more training and expertise. In this case you will need to access the MSDS’s available in the workplace chemical register and find important information.

6  

2 FIRE SAFETY  

PURPOSE  

To demonstrate key points in fire safety including the use of portable fire extinguishers, fire evacuation procedures, and general housekeeping to reduce the risk of fire. This chapter addresses the following learning outcomes: • recognise laboratory fire hazards and perform risk assessment procedures • implement fire control measures to minimise the risks associated with hazards

found in the laboratory • identify and implement appropriate procedures to deal with emergency situations

concerning laboratory fires • extinguish fires, and describe appropriate procedures to deal with emergency

situations relating to them.  2.1 WHAT IS FIRE?

 

A fire occurs when flammable materials are heated to the temperature at which they ignite in the presence of oxygen. The source of oxygen is generally air. Only vapours burn, so solids and liquids must be aporized before combustion can occur.

 2.2 THE FIRE TRIANGLE

 

To start a fire three components must be present: 1. air (or a source of oxygen) 2. fuel 3. heat

 

These are the components of the so-called fire triangle. While all three of these components are present, a fire will be maintained. Removal of any one will result in the fire being extinguished.

 

 

Fuel

 

For a fire to be sustained, the three components must also be present in the correct ratios. Examples of this include the arburetor of your car, where if your fuel-to-air ratio is not just right the spark does not ignite the mixture in the cylinder of the engine, or the gas stove in your house where if there is not enough gas (or air), the flame will not ignite. The area over which the fire is spread is another important consideration. If the fire is contained in a small area then a small fire will result, But a much greater fire risk (and greater fire intensity) will occur if the same amount of fuel is spread over a larger area. This is because the greater surface area provides a better oxygen supply to feed the combustion process. In short, the larger the surface area, the worse the fire.

 When using chemicals, a not-so-obvious source of heat is an uncontrolled chain reaction. You should be particularly wary about any chemical substance which can polymerise rapidly as this may cause a fire.

7  

2.3 TYPES OF FIRES  

Fires are generally classified into groups according to fuel type; these are shown in Table 2.1. These classifications are useful as a guide for fire extinguisher selection.  

Table 2.1 The different classes of fire and their fuel type

Class Fuel type

A

B

C

D

E

F

General combustible materials such as wood, paper and fabrics.

Flammable liquids such as paint, varnish or mineral oil.

Flammable gases such as ethyne (acetylene) or hydrogen.

Combustible metal such as magnesium or titanium.

Electrical sparks and heat from current flow.

Fat and cooking oil.  

Fire extinguishers are not universal. The correct selection of type, and the correct use of extinguisher is vital in order to successfully extinguish a fire.

 2.4 STRATEGIES TO FIGHT FIRES

 

If we remove one of the components of the fire triangle, a fire is not sustained, hence this serves as an obvious means of fighting fires. This gives us three main strategies to fight a fire:

Cooling – with water or other agents Starve it of fuel – only practical in some cases Smothering or diluting – the air or oxygen supply.

 Cooling – a method normally used on class A fires. Water is the least expensive and most commonly used extinguishing agent. Its success in this area is due to its great capacity to absorb heat. The primary effect of water is to remove the heat from the fire, but often some smothering also occurs when the water turns to steam and displaces the air (oxygen) above the fire. If the fire is deep seated, as often occurs in class A fires, cooling is generally the most appropriate strategy for extinguishment.

 Starving of fuel – this method is rarely applied unless access to a supply valve of a pipe or the equivalent is easily accessed.

 Smothering – a technique generally used in fighting class B, C, D, E and F fires. Non- combustible gases such as carbon dioxide (CO2) or Inogen (a mixture of nitrogen and CO2), ressurize liquids such as NAF S3 and BCF (bromochlorofluoromethane), or even dry chemical powders that generate CO2

when burned may be used.  2.5 TYPES OF FIRE EXTINGUISHERS There are many different types of fire extinguishers. Table 2.2 lists some common ones and also shows their suitability for each class of fire. Because wet chemical and special purpose (Met-L-Ex) extinguishers are rare, they have not been included in the Table 2.2. Wet chemical extinguishers are suitable for class A and F fires only. More information on portable fire extinguishers and fire blankets including selection and location is provided by Standards Australia. The University uses mainly two types of extinguishers, most commonly Dry Chemical, and Carbon Dioxide. Water is available from hose reels installed in the buildings. There are some fire blankets installed in the laboratories in some of the buildings. Therefore, these types of extinguishers are described briefly in the next few sub-sections.

8  

Table 2.2 Fire extinguisher selection chart

Class of fire Type of extinguisher and colour code

    H2O Foam CO2 Dry Vaporising

        chemical liquid

  Red Blue Red with Red with Red with

      black band white band yellow band

A General combustables

B Flammable liquids

A

C Flammable gases

D Combustable metals B B

E Electrical *

F Fat and cooking oil  

Key: most suited may be used not suitable A Can be used, but may cause damage to expensive electrical components. B May be used in an emergency, but not very effective. Sand or Met-L-Ex are more

effective. Some combustible metals react with CO2. * Not suited to fat or cooking oil fires.

  1) Dry Chemical Powder Fire extinguisher – Colour RED with a WHITE BAND This is probably the most useful fire extinguisher of all, in that it is suitable for almost all fires and is capable of controlling more fire area on a weight-to-weight basis than any other. These extinguishers contain ressurized gas and a powder rich in carbonate which generates carbon dioxide upon heating in the flames.

 2) Carbon Dioxide Extinguishers – Colour RED with a BLACK BAND These contain compressed carbon dioxide, which is a dense non-conducting gas. It extinguishes the fire by forming a dense blanket over the flames and excluding oxygen. As it is a gas, it is ideal for use in inaccessible places. It is also non-corrosive and hence may be used without damaging most equipment with the exception of computers.

 Carbon dioxide extinguishers do have some disadvantages. They are not recommended for use in confined spaces (as carbon dioxide is an asphyxiant gas), and their extremely low operating temperature means that they can damage skin and valuable computing equipment. 3) Sand This is often a viable and inexpensive alternative for extinguishing small fires. A layer of sand (or earth) will deny the fire essential oxygen. It is particularly useful in class D fires.

 4) Fire Blankets These are generally used for extinguishing fires on people. The correct technique for use is to approach the burning victim, raise the blanket up in front of you to protect your face, and completely wrap the victim inside the blanket.

 If you catch fire in the laboratory DO NOT RUN. If a fire blanket is not readily available roll on the ground or use a safety shower as quickly as possible. A good non-combustible laboratory coat should afford a very temporary protection from fire, enabling extinguishment before major tissue damage occurs.   

9  

  2.6 EXTINGUISHING FIRES

 

Before attempting to control a fire by using a portable extinguisher, you must be aware of how to use it correctly. An incorrectly tilized extinguisher, or the use of the wrong type of extinguisher can at best have little effect on the fire or at worst spread the fire over a larger area making it even harder to extinguish. A useful mnemonic to help remember the correct way to use a portable fire extinguisher is PASS.

  Pull the safety pin to allow the trigger to be pressed.

Some extinguishers may require other special actions. Aim low and direct the extinguisher towards the base of the fire. Squeeze the handle to release the extinguishing agent. Sweep the extinguisher from side to side at the base of the fire

until it has been extinguished.  

2.7 WORKPLACE EVACUATION  2.7.1 In the Event of a Fire or Other Emergency, What Should You Do?

 In a large workplace, the evacuation will be controlled by a Building Evacuation Officer and floor wardens. These are trained personnel who together will control all aspects of the building evacuation. You should quickly, but calmly, follow the instructions of the floor warden and assemble at the designated meeting place (a safe place near the area with no risk to personal safety).

 You should stay at the meeting place until advised to leave by the site controller, or emergency services personnel. This is the only way to ensure that no one remains in the burning building and requires rescuing. If you leave the meeting place without permission, you may unnecessarily endanger the lives of emergency services personnel who will be required to attempt to rescue those thought to remain in the burning building.

 All large workplaces should have a standard evacuation plan. Regular practice of the drill is advised to ensure staff familiarity for greater safety in the case of a genuine emergency.  

Assembly Points, as well as lists of Evacuation Officers are listed on notice boards and on walls throughout the University buildings.

 

2.7.2 Procedures for Smaller Workplaces In smaller workplaces you should follow the simple instructions which are outlined in the RACE principle.

 

Rescue or assist any persons in immediate danger.

Alarm. Raise the alarm and follow your emergency procedures. This should include notifying the switchboard or office of the danger, or if you have one notify the floor

10  

warden or site controller. If this is not possible notify emergency services (such as the fire brigade) yourself.

The phone number of the fire brigade should be prominently displayed in all workplace areas. Clear and precise details of the exact location of the fire MUST be given to emergency services.

 

Contain the fire. Appropriate measures include the sealing off of the fire by closing all doors and windows.

Evacuate all non-essential personnel to the emergency meeting place. Attempting to extinguish the fire should only be attempted if it safe to do so and if you are trained in the use of fire safety equipment.

 THE DO'S • All people should be evacuated using the normal evacuation drill and should

assemble for counting in the designated areas. • Power should be cut to the area concerned. • Extinguishers and hoses should only be used if the fire is small or can be accessed safely

and by trained personnel. • Once evacuated all doors and windows should remain shut to limit access of oxygen to

the fire. This will greatly restrict its progress. • All vehicles and other sources of ignition should be moved from the area if possible. • If a person catches fire, roll them in a rug or lab coat to smother the flames. • When escaping from a fire in an enclosed area keep low to the floor and do not

breathe the hot gases if possible.  THE DON'TS • Do not open a closed door without feeling if it is hot. • Do not use a lift to escape a fire. • Do not re-enter a burning building.

 2.8 GOOD HOUSEKEEPING - MINIMISING FIRE HAZARDS

 

The risk of fire in the workplace may be greatly decreased by taking some simple precautions in your workplace. In particular you should ensure that:

  electrical circuits are not overloaded, and power is wired up in the

correct fashion smoking is not permitted in areas where flammable liquids may be used flammable liquids should not be stored near heat sources and larger

volumes should be stored in flameproof cabinets. There are statutory requirements for storage of flammable liquids

fire exits are not obstructed sprinkler or smoke alarm systems are not obstructed the correct type and an appropriate number of fire extinguishers are

available regular maintenance of fire safety equipment is carried out regular fire drills are carried out.

 You should carefully examine your work area to see if you are doing all that you can to minimise the risk

11  

3 ELECTRICAL SAFETY  

PURPOSE  

To explain the nature of electricity, and demonstrate important aspects of electrical safety including terminology, handling of electrical equipment, and housekeeping procedures to reduce the risk of electrical accidents.  This chapter addresses the following learning outcomes: recall and interpret important terms and information relating to electrical safety, implement control measures to minimise the risks associated with electrical equipment found in the laboratory, demonstrate safe work practices with electrical equipment.

 3.1 WHAT IS ELECTRICITY?

 

Electricity is a general term which refers to any phenomenon relating to electric charges. It may be produced by chemical means (such as a battery) or it may be produced by physical means such as rubbing an insulator, or rotating the coils in a generator (as occurs in power stations). Regardless of how it is produced, its nature is still the same.

 3.2 SOME IMPORTANT ELECTRICAL TERMS

 

Circuit- a path through which electrons flow from a high voltage to a lower voltage. In electrical accidents, people become part of the circuit and allow electrons to flow through them before returning to the power station via the earth. Conductor - any material which allows electrons to flow through it. Current - a flow of electrons along a conductor. Its unit is the ampere and its symbol I. Current comes in two forms: DC current (the type obtained from a battery) where electrons all move in one direction along the conductor; and AC current (alternating current) where the electrons move backwards and forwards along the conductor. Earth - an electrical connection to the ground source (such as a power station) to complete a circuit that provides a return path to a voltage electrical circuit. Arbitrarily assigned a value of 0 volts. Electric shock - a condition that occurs when an electric current from an external source passes through a living body. Electron - a small particle of matter that carries a negative charge. Insulator - any material that does not allow electrons to flow through it. Live - any circuit that has a voltage applied to it Resistance - when a current of electrons flows through a material the material resists the flow to some extent. Some of the energy of the electrons is generally lost as heat

in the process. The unit of resistance is the ohm and it is given the symbol or R. Short circuit - a condition where part of an electrical circuit is by-passed and the current takes a different route to that originally intended. This may lead to electrical equipment becoming live and then causing electric shock when touched. Voltage - (also known as electromotive force or EMF) refers to the difference in potential energy of two bodies connected by a conductor. More simply, it is the pressure driving the

electrons through a conductor. The unit of voltage is the volt and it is given the symbol V. 3.3 THE RELATIONSHIP BETWEEN VOLTAGE, CURRENT AND RESISTANCE

 

The terms voltage and current are often incorrectly used (sometimes interchanged) when

12  

inexperienced people talk about electrical equipment. For this reason we will examine some simple analogies to help explain their meanings. The best analogy relates electrical terms to water flow.  Firstly, voltage, current, and resistance are all related via an expression known as Ohm’s law. Voltage is the product of resistance and current, that is V = IR, hence you cannot change one without affecting the others in a closed system. From the equation you may deduce that a combination of high voltage and low resistance will cause a large current to flow. This is the situation where most electrical accidents occur.  The flow of electrons along a conductor (current) may be likened to the flow of water through a pipe. Pressure is needed to force water through a pipe and likewise a voltage (a pressure caused by a store of electrons of higher energy) is required to push electrons along a wire. To take the analogy further, we can examine the flow of water from a reservoir to your tap. Water in the reservoir is located on a hill. We all know water flows downhill through the pipes from high potential energy to low potential energy and hence when the tap is opened water pressure forces it out. In a similar fashion when a power switch is turned on, electrons at the power station, or in a charged battery (a high energy state) flow through a conductor (the power leads) to electrical devices which use the electrons’ energy. The pressure forcing the electrons along the wire is the voltage, while the actual flow of electrons is the current. Anything that retards the flow of the electrons is referred to as resistance. If a battery is the source of electrons, the flow will continue until there is no difference in energy between the battery’s electrons and those in the device. This is what is known as a `flat battery’. Table 3.1 relates the similarities between the flow of water and that of electricity.

 3.4 ELECTRICAL ACCIDENTS  

These may result from either the direct effects of electrical current flowing through a person, or from the indirect effect of an electrical shock where the victim sustains an injury from an associated fall or accident.  Electricity kills by paralysing the breathing system, causing heart malfunction, and 'cooking' the internal organs.

 Table 3.1 A quick summary of electrical terms

Term Units Symbol Meaning Analogy

Voltage Volts V The difference in potential energy between one point and another.

Water pressure in a pipe

Current Amps I The flow of electrons from one point to another

The flow of water through a pipe

Resistance Ohms R Any force which opposes the flow of electrons

Obstruction in a pipe

13  

Two factors determine how serious an electric shock is to the body: the total amount of current which flows, and the time for which the body is exposed.  

Degree of injury = amount of current x time of exposure  For this reason you should remove a victim of electric shock from the source of electricity as soon as possible to inimize injury.

 3.5 WHICH IS WORSE, HIGH VOLTAGE OR HIGH CURRENT?

 

You may think that 1,000 V would be more deadly than 100 V, but this is not necessarily true. The normal household voltage of 240 V is responsible for most deaths associated with electrical shock. Deaths have occurred with DC shocks of only 42 V. Remember, the real measure of the intensity of an electrical shock lies in the amount of current to which the body is exposed. You may all remember playing with a Van de Graaff generator at school (that big silver ball with an oversized elastic band inside which makes your hair stand on end when you touch it). This device operates at 10,000 V, but the current associated with this is minimal, so it can be used for party tricks safely. This is because the high voltage is associated with high resistance. In general however, most high voltage devices must be treated as very dangerous because if they find a path of low resistance to return to their source (such as through your body) a very large current will flow, generally resulting in electrocution. The combination of high voltage and high current is extremely dangerous. Devices in this category should only be handled by those who are properly trained.  3.6 WHAT IS A FATAL CURRENT?

 

The lowest current which can be felt by the average person is between 0.8 to 1.2 mA (milliamps). This is referred to as the threshold of sensation and is unlikely to cause any damage to body tissue.  A current of around 2-10 mA will cause a person to pull away from an object. This is associated with most fall injuries. The brain sends messages to the muscles via low current electrical impulses. Current in the range 10 to 100 mA will override these signals. In this situation, you cannot let go of the source of the current as the brain can no longer communicate with the muscles, which instead respond to the external electrical stimulus. For this reason it is suggested that you test electrical apparatus with the back of your hand before operation. This prevents a grip response from your hand which then can’t let go of the device.  Exposure to currents between 100 and 200 mA generally causes death. This is because the heart goes into ventricular fibrillation, where it ceases to pump and goes into a quivering motion. This condition can only normally be reversed by a special device known as a defibrillator. Electrical shocks with current flows of greater than 200 mA lead to symptoms similar, but far more exaggerated than those received in the current range from 10-100 mA. Surprisingly, a person is much more likely to survive a shock of 500 mA than 150 mA. This is because the heart is likely to clamp shut under higher current and hence does not go into fibrillation. Table 3.2 shows the effect of different levels of current on the body. Note that voltage is not a consideration. Effects vary with AC or DC currents and from person to person so these must be treated as approximate only.

 3.7 OTHER FACTORS IN ELECTRIC SHOCK

 

The path that the current takes through the body also determines the amount of damage sustained by a victim of electric shock. This is because the electrical current may travel through vital organs in the body causing them to be damaged. If this damage is bad enough the organs

14  

will cease to function and life will be threatened. Predicting the internal damage caused by electric shock is not easy, but it is very likely that the respiratory control centre in the brain will be affected and breathing will stop. If this occurs, brain damage due to lack of oxygen will occur within 2-4 minutes. The victim is also likely to sustain muscular paralysis and extreme pain (due to the burning effect of the current). If cardiopulmonary resuscitation (CPR) is applied within two minutes after the shock occurs, the victims chances of recovery are much greater.

 

  

Table 3.2 The effects of different levels of current on the body

Approximate current level (mA)

Effect on body

0.8-1.2

2-10

10-100

100-200

Above 20

Threshold of sensation. Little or no damage is sustained.

Pain and response to pull away from object. The cause of many falls.

Causes muscles to clamp. May lead to hands gripping conductor with the victim unable

to let go. Pain and burn damage increases with current.

Generally causes death by sending the heart into ventricular fibrillation. Victim does not

generally respond to first aid.

Leads to muscular paralysis, extreme burns and pain. Does not necessarily cause

death as victim may respond to first aid, but higher current levels will generally kill

victim without swift action from rescuers.   

 

Current path through vital organs

Electrical current will take the path of least resistance through your body. It is difficult to estimate the resistance between different parts of your body as this varies greatly according to health and environmental conditions. Hence it is difficult to predict the exact path that a shock has taken. Often internal organs may be damaged while the victim outwardly appears to be in perfect physical order.

 3.8 TREATMENT OF VICTIMS OF ELECTRICAL SHOCK

 

Too often a person trying to render assistance to an electrocution victim is also electrocuted. Do not touch a person who is in contact with a live power source, as this will lead to you also becoming part of the circuit and being similarly affected. The best approach is to turn off the power if this is possible, but don’t waste time looking for the power switch if it is not accessible as it is important to remove the victim from the source of current as soon as possible.

15  

Try to dislodge them from the source of power without endangering your own safety. A dry length of wood can often be used to `prod’ a victim and remove them from the live power source.

 Insulate yourself from earth so that a current will not flow through your body (remember the old rubber soles!). Also insulate yourself from the power and the victim before attempting to remove them from the source of electrocution. Rubber gloves or leather materials are good insulators, alternatively dry timber or clothing may be used. If there is no other alternative, striking the victim with a swift blow from the hands or feet may be considered as a last resort, but if this is necessary avoid direct contact with the skin. After successfully removing a person from a live power source, resuscitation can be commenced if they have stopped breathing or medical treatment may be given if they are conscious.  Because of the possibility of internal organ damage it is advisable to refer all victims of electrical shock for medical treatment.

 3.9 GUIDELINES FOR PREVENTION AND CONTROL OF ELECTRICAL ACCIDENTS  

Commonsense and care and a few basic techniques will greatly decrease the likelihood of you being involved in an electrical accident. The points which follow list appropriate actions to minimise the likelihood of an electrical accident in your workplace. • Do not use instruments with frayed or damaged power cords, and do not overload

power points. • Report all defects or accidents with electrical equipment. • Touch all electrical equipment with the back of your hand before use. This will

prevent you accidentally gripping the device if it is live. • Install circuit breakers on all power supplies. • Apply danger tags (also known as safety tags) or locks where required. These are

used to prevent the operation of faulty equipment. If you find a piece of equipment which is faulty or unsafe, you should switch it off and tie a danger tag to the isolation switch. If the equipment is equipped with lock-out isolation it should be used in addition to the safety tag. This prevents operation until the problem is fixed. Only the person who fitted a danger tag is allowed to remove it. Never use any piece of equipment fitted with a danger tag. If you are required to isolate the component from other electrical devices to render it inoperative, then you should also attach a danger tag to the main power switch or circuit breaker.

16  

 

• Install earth leakage core balance current breakers (also known as safety switches) where possible. These monitor the current into, and out of a circuit, and when they are not equal (such as when a person is providing an alternate route for return of electrons to the power station through their bodies, i.e. they are being electrocuted) they switch the power off.

• Do not attempt repairs on equipment with which you are not familiar or have no expertise.

• Wear insulated footwear (or work on insulated flooring or mats). This prevents you from providing a path for electron flow to earth through your feet.

• Ensure all power points are off when plugging in or disconnecting devices. • Do not store flammable substances near control panels, fuse boxes or electrical

equipment which may cause a spark. • Avoid wearing jewellery or large belt buckles when operating electrical devices, as these

are excellent conductors. • Try to avoid using extension cords, but if you must use them ensure that they are fully

unwound to prevent overheating. • Remember water and electricity do not mix. Electrical appliances should not be used with wet

hands or feet. • Electrical current always takes the path of least resistance. Do not allow your body to

become part of this path.  

WHAT YOU NEED TO BE ABLE TO DO  Recall important terms relating to electrical safety. Discuss factors which influence the degree of injury sustained in accidents. Describe methods for the treatment of victims of electrical shock. List methods for the prevention of electrical accidents in the laboratory.      

17  

This page is intentionally left blank

18  

Student Answer Sheet

Student ID_______________

Last name________________ First name___________________

Prac Class: Day …………… Time …..… Demonstrator ………………………

FIRE SAFETY  

Q1 In case of emergencies you should know your location. Why?  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….

Where are you now ? Bldg-Room: …………..

 Q2 Where is the closest fire extinguisher?  

…………………………………………………………………………….

What type is it?

…………………………………………………………………………….

What sort of fires is it best suited for use on?

…………………………………………………………………………….   Q3 If there was a fire alarm right now, where should you go?  

…………………………………………………………………………….  

…………………………………………………………………………….   Q4 If there was a fire in the laboratory, what could you use to fight the fire besides an extinguisher?

…………………………………………………………………………….   Q5 What are the conditions and components required for a fire to be sustained?  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….   Q6 What are the three different strategies to fight fires?  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….    

19  

ELECTRICAL SAFETY  

Q1 When working with electrical circuits, your physical condition and appearance is important. Name two things that would put you at risk from an electrical safety perspective and thus must be avoided.  (1) ……………………………………………………….  

(2) ……………………………………………………….  

 Q2 Is there an emergency stop/isolation switch in the laboratory? Yes / No

If so, where?

…………………………………………………………………………….  

…………………………………………………………………………….   Q3 Your inquisitive practical partner gets his bushy eyebrow caught in an electric motor. You should,  

A leave him be, because the practical was about electrical testing. B leave him be, because you do all the work and he does nothing every prac. C yank him back quickly, the quicker the better D turn off the motor in the quickest manner possible and contact security.  Q4 What are the two factors that determine the degree of damage sustained by a person during an electric shock?  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….   Q5 Why would someone who works with dangerous electrical devices on a routine basis touch all devices with the back of their hand?  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….  

…………………………………………………………………………….   Q6 Complete these statements:  

Deaths have occurred with DC shocks as low as …….….. V.  

The intensity of an electrical shock lies in ………………………………  

……………………………………………………. the body is exposed.  

A circuit is live when …………………………………………………..

A current of ………………mA causes muscles to cramp.

Brain damage due to lack of oxygen will occur in ……..……minutes.

20  

LABORATORY FIRST AID  

Q1 What phone number/s should be called in case of an accident in this laboratory? …………………………………………………………………………….

 

…………………………………………………………………………….  

Q2 A silly student returns from the toilet after washing their hands (the dryer was not working) and connects their circuit to the mains power GPO then proceeds to turn it on. Most naively they connect a step-up transformer with wet hands. Soon their long hair is standing straight up from their head. As they spasm, the odour of shorted electronics fills the air. You notice the smell and look up. What do you do?

 

…………………………………………………………………………….  

…………………………………………………………………………….  

The student is unconscious, what now? ……………………………………………………………………………. GENERAL SAFETY Q1 Why should food and drinks be excluded from the laboratory? ……………………………………………………………………………. ……………………………………………………………………………. ……………………………………………………………………………. ……………………………………………………………………………. Q2 Identify 3 safety issues evident in the photo on the left of a man drilling a hole in the roof. ……………………………………………………………………………. ……………………………………………………………………………. ……………………………………………………………………………. …………………………………………………………………………….

21  

DECLARATION Name: ........................................................................................ ID No: ............................................ I declare that I have undertaken the full OH&S exercise, that I have answered the questions on this record sheet conscientiously and that I accept responsibility for my actions at all times in teaching laboratories within the School of Engineering at the University of South Australia. I further declare that I am aware that supplementary safety information is supplied in the front section of practical manuals and that it is my responsibility to familiarise myself with said information and equipment referred to in those documents. Signature: .......................................................................... Date: